Often times after steel sheets are hot formed to create a semifinished product they are also then subjected to a hardening process. The hardening process may cause surface damage and/or corrosion to occur in the sheet metal. To prevent such surface damage and corrosion from occurring in hot formed steel sheets when they are subjected to a hardening process, prior to the hot forming step the steel sheets may have a protective layer applied thereto, or created therein. A common method is the coating of the steel sheets with an anti-corrosion coating (metal coating), such as an aluminum-silicon alloy (AlSi), for example, in the context of hot-dipping of steel strips.
However, during the welding of such coated steel sheets, aluminum inclusions can occur in the weld seam, with the undesirable result that the strength of the welded connection is decreased or compromised. It is therefore necessary, after the hardening process, to remove the metal coating from those regions of the steel sheet in which a welded connection is to be made. In particular the edges of the steel sheets usually represent the regions to be decoated. However, edge preparation may be necessary not only in the case of coated steel sheets, but also in the case of uncoated steel sheets that are intended to be fed to a welding process, and may be, for example, coated in oil or other surface contamination and/or in an already slightly corroded state.
In order to remove the metal coating from the steel sheet, the document DE 10 2011 050 316 A1 proposes a method in which the steel-sheet blank is placed on a blank support of a press and during a closing movement of the press, scraping knives are moved transversely to a main direction of extent of the regions to be decoated of the blank in order to scrape off the coating of the blank in these regions. The regions of the blank to be decoated usually comprise the edge regions of the blank. The scraping knives are pushed into the layer during the closure of the press and subsequently pulled out or moved as far as the edge perpendicular to the edge profile. Depending on the steel-sheet contour, the edge regions can also have relatively complex profiles with comparatively small curve radii. On account of the unfavorable angular position, it is disadvantageously not possible to decoat such steel-sheet contours having highly curved edges using the proposed method. Furthermore, in the proposed solution, there is the problem that it is comparatively difficult to set the scraping knives exactly over a relatively great length.
A further solution for removing the metal coating from only one side of the steel sheet can be found in the document DE 10 2006 050 702 A1, in which provision is made of a machining tool of the plane type or rotating grinding head type which acts areally on the surface of one side of the steel strip in order to effect mechanical stripping of the metal coating there. A disadvantage with this solution is that only one side of the metal coating is stripped off. Furthermore, this solution is configured to achieve areal stripping of the metal coating from the entire surface of the one side of the steel sheet, with the result that the precise positioning, necessary for partial decoating, of the machining tool relative to the steel sheet is realizable only in a comparatively complicated manner.